I simply tried to find a suffix of the path that still identifies the element uniquely. Turns out that p:nth-of-type(3) is good enough already. If you want to be a bit more robust to changes on the page, you could also search for the last element with an ID in the path, i.e. #mw-content-text > div.mw-parser-output > p:nth-of-type(3).
If you mean what I think you mean, you can already send a link that specifies a valid element ID on the page to anybody and have their browser focus on it — that's what fragment identifiers are for. However, if the page designer has neglected to provide a unique ID for each page element (and they probably have), you're out of luck. Ideally, you'd be able to specify any valid CSS selector that only selects one element as a fragment identifier, but that's not the case (and is basically what this extension makes possible).
Would an XPath work for this? Seems like that would be easiest considering Firefox already has built-in support for getting the XPath from an element on the page.
(I wasn't kidding about needing to shorten those links.)